There is little change to the spatial pattern of global SSTs from a week ago. An earlier trade wind surge across the west central Pacific Ocean responding to the MJO did slightly weaken the warm anomalies around the equatorial Dateline. However, the thermocline slope remains less than normal and, loosely, slightly positive SSTs extend along the equator from Indonesia to South America. Warmest ocean waters globally (greater than 30C) continue just east of New Guinea as well as in pockets across the North Indian Ocean including both the Arabian Sea and Bay of Bengal.

One of the many ENSO issues includes the magnitude of (any) additional warming across the west Pacific Ocean during the next several months. In short, if there is to be a respectable El-Nino this upcoming boreal cold season, I am still not impressed by what I am observing. For instance, tropical convective forcing is “hanging back” north of the equator centered on the Bay of Bengal (more said below). There are also too many global circulation La-Nina characteristics that are impossible for me to address here. The atmospheric component of the weather-climate dynamical system may again call the “Nino SST shots” after this summer.Please remember that ENSO is an interannually evolving global phenomenon impacted by interactions across multiple time/space scales (including GWO dynamics/processes), not ONI.See links below.

There is also no change to the painful complexity, including the harsh reality that now is not a good time to be making weather predictions. Tropical convective forcing remains most intense across the Eastern Hemisphere. However, there are now arguably 2 regions, one centered in the Bay of Bengal (BB; including a tropical cyclone attempting to develop) and the other ~0/155E.The MJO component, as a continuation from the April event, is still propagating eastward ~10-12m/s leading to the west Pacific Ocean flare-up. The enhanced rainfall centered on the BB was left in the wake of the MJO, and is likely contributing to the onset of the regional-scale monsoon systems. All things considered, in addition to the possibility of the return of the nemesis of 2 convective regions discussed in the past, I am also concerned the quasi-stationary La-Nina tropical signal may be attempting a comeback. Again, the global financial markets are a great analogy. Just like we are still in a major bear stock market with economic issues will take some time to resolve, in terms of AAM the atmosphere still has significant bearish signals.Perhaps it is time to “short” the recent global AAM rally!

The combination of the winds and convective signals has led to a resurgent MJO signal in WH (2004) phase space, having ~1.5 sigma projection in octant 7 (through 22 May) and somewhat weaker in octant 6 retaining ENSO. The “loop scenario” offered in my 16 May discussion worked out.Phase 6 of the 250mb MJO snr psi composite anomaly plots best describes tropical and even a few extratropical circulation anomalies. My thought has been for this signal to persist in octants 6-8 for a while. However, there may start to be cancellation between the 2 regions mentioned above. Regardless of the projection, I still do expect a signal of tropical forcing to propagate through the Western Hemisphere during the next few weeks. Stay tuned as the mixed signals mess continues.

Tropical-extratropical interactions including the MJO and dynamical processes explained by the WB (2009) measure of the GWO have worked to create a recent respectable positive global wind tendency. Through 21 May global AAM tendency was ~plus 20 Hadleys having large zonal mean contributions from the equatorial and subtropical atmospheres. In fact, latest 250mb weekly means are ~3-4m/s.However, albeit shifted northward, 250mb weekly averaged zonal mean easterly wind flow anomalies are ~10m/s around 45-50N, strongly bearish.

Forced by AAM transports (see plots), those poleward and downward propagating anomalous zonal mean easterly wind flows have increased global and zonal mean mountain and frictional torques during the past 7-10 days. That has also contributed to the recent increase in global westerly wind flow with relative AAM near the R1 data climatology. The point from this untangling of the earth-atmosphere AAM budget is that there is finally a greater than 1 sigma projection of the GWO. Through 21 May the signal was in octant 4-5 of phase space. However, I am not at all confident there will be the nice GWO variations in the near future like observed during this past boreal cold season. There may be a weak orbit towards octants 7-8-1; however, hanging around toward phases 3-5 UFN appears probable (weak La-Nina). Phase 4 of the GWO 250mb snr psi composite anomaly plot reasonably describes the current global atmosphere.

Synoptic responses during the past week or so included the zonal mean storm track shifted anomalously poleward over the Northern Hemisphere, continuation of anomalous extratropical ridges (both hemispheres) with low pressure across the subtropics, and Western Hemisphere subtropical jets. Cutting to the chase, I do expect the latter to shift poleward and bring the Northern Hemisphere storm track southward (including the lower 48 states) over the next 2-3 weeks. During roughly days 10-20 a couple of strong progressive troughs across the western into the central states (north of ~35-40 degrees) is still possible should there be some form of GWO 7-8-1 transition. Maybe there is still some hope for project VORTEX!

I am continuing the notion I have had since mid-April about the average synoptic pattern across the USA during JJA.This is as depicted by roughly a superposition of GWO/MJO phases 3-5 (weak La-Nina atmosphere) of the 250mb snr psi composite anomaly plots centered on 15 July. As previously typed, that is suggestive of ridges near both coasts with some form of a trough in the middle of the country ~85-90W. Of course, a bit more global westerly wind flow and this pattern could be the reverse! Weather impacts, nationally and internationally should be understood from the composites.

Appendix

All presentations from the 24 February 2009 GWO workshop are available via anonymous ftp. If you have not received information on how to retrieve these, let me know. There was excellent attendance at this day-long event, and feedback was strongly positive. We are working HARD to mainstream this effort. The support is very much appreciated!

Links to CPC and PSD ENSO discussions, and a new experimental forecast technique involving a coupled LIM (3rd link below):

These are probabilistic statements. We hope that an opportunity will arise for us (soon) to allow our dedicated web page effort to mature, expediting objectively and accountability. This web page effort will hopefully include an objective predictive scheme for the GWO with hindcasts.

The WB (2007) paper on the GSDM has been published in the February issue of MWR. The first of a two-part paper, where WB formally introduce the GWO (WB (2009)), is (still) awaiting publication in MWR. An early on-line release can be downloaded from the following link:

In addition to the subseasonal snr composite anomaly plots, we would like near real-time discussions with “weather maps” to become a routine part of the ESRL/PSD GSDM web site sometime soon. Part-2 of our GWO paper will discuss the latter. We want to emphasize notions such as global-zonal mean-regional scale linkages as well as forcing-response-feedback (with subsequent interactions) relationships. An important purpose is to provide a dynamical weather-climate linkage framework to evaluate the numerical models in a sophisticated manner as part of a complete subseasonal (and any time scale) forecast process, in addition to a climate service for all users. Relying on the numerical models alone is a cookbook, extremely unscientific, and makes Rex the Rottweiler VERY angry! I will not be able to do a complete discussion until the weekend of 5-7 June.Anyway, I need a break from all this atmospheric madness!

4 comments:

If there was to be cooling in the west Pacifc Ocean and if the convective forcing in the BB was to die down, how much more would it take for you to consider El-Nino a possibility for this upcoming winter?

How does propogating easterly wind flow from 45-50N lead to an increase in global westerly wind flow?

To me the aspect of JJA being dominated by ridges on the coasts is exciting.

First, if you want an El-Nino, a warm west Pacific Ocean is a good thing. For ex., wwbs with tropical forcing could excite downwelling oceanic Kelvin waves to warm the entire basin. My concern is should EH tropical forcing continue to dominate especially this fall, trade surges may lead to cooling perhaps similar to 2008. We will have to monitor all this.

Much of the increase in global westerly wind flow has come from the equatorial/subtropical regions. Zonal mean anomalous easterlies have been propagating poleward as a response. See AAM plots, especially

So, you are concerned with the whole "what goes up must come down" aspect of the convective forcing. They could cause the warming of the west Pacific, but if they last too long, there could be a strong response cooling off the west Pacific.

Looking at the link you posted, I can see that from mid- April until recently that the easterly winds have been moving towards the poles. I see what you are saying with the poleward propogation of easterlies.

That is one way of putting it. An important issue is to build up heat content. Right now conditions across the eq. west Pacific are favorable. Convection is minimal and the trades are weaker than normal. Should the trades strengthen responding to enhanced convection farther west (ex., N. IO, active monsoon systems, etc.), that may offset warming. Regardless, we need to monitor. Compared to a year ago, an El-Nino (at least early stages) is more probable for 2009-10.